Electric power generation method using thermoelectric power generation element, thermoelectric power generation element and method of producing the same, and thermoelectric power generation device

ABSTRACT

The present invention provides an electric power generation method using a thermoelectric power generation element, a thermoelectric power generation element, and a thermoelectric power generation device, each of which has high thermoelectric power generation performance and can be used for more applications. The thermoelectric power generation element includes a first electrode and a second electrode that are disposed to oppose each other, and a laminate that is interposed between the first and second electrodes and that is electrically connected to both the first and second electrodes, where the laminate has a structure in which SrB 6  layers and metal layers containing Cu, Ag, Au, or Al are laminated alternately, a thickness ratio between the metal layer and the SrB 6  layer is in a range of metal layer: SrB 6  layer=20:1 to 2.5:1, lamination surfaces of the SrB 6  layers and the metal layers are inclined at an inclination angle θ of 20° to 50° with respect to a direction in which the first electrode and the second electrode oppose each other, and a temperature difference applied in a direction perpendicular to the direction in the element generates a potential difference between the first and second electrodes. The electric power generation method and thermoelectric power generation device each use the element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power generation methodusing a thermoelectric power generation element, which is a method ofobtaining electrical energy directly from thermal energy. Furthermore,the present invention also relates to a thermoelectric power generationelement that converts thermal energy directly into electrical energy andthe method of producing the same, as well as a thermoelectric powergeneration device.

2. Description of the Related Art

Thermoelectric power generation is a technique for converting thermalenergy directly into electrical energy by utilizing the Seebeck effectwhereby an electromotive force is generated in proportion to thetemperature difference applied to both ends of a material. Thistechnique is used practically in, for example, remote area power supply,space power supply, and military power supply.

A conventional thermoelectric power generation element generally has astructure that is referred to as a so-called “π-type structure”, inwhich a “p-type semiconductor” and an “n-type semiconductor” that aredifferent in carrier sign from each other are combined togetherthermally in parallel and electrically in series.

Generally, the performance of a thermoelectric material that is used fora thermoelectric power generation element is evaluated by a figure ofmerit Z or a figure of merit ZT nondimensionalized by multiplying Z byabsolute temperature. ZT can be expressed by a formula of ZT=S²/ρK,where S denotes the Seebeck coefficient of a thermoelectric material, ρindicates electrical resistivity, and κ is thermal conductivity.Furthermore, S²/ρ, which is an index expressed with consideration beinggiven to only the Seebeck coefficient S and electrical resistivity ρ,also is referred to as a power factor (output factor) and serves as acriterion for evaluating the power generation performance of athermoelectric material obtained when the temperature difference isconstant.

Bi₂Te₃ that currently is used practically as a thermoelectric materialhas a high thermoelectric power generation performance, specifically, aZT of approximately 1 and a power factor of about 40 μW/(cm·K²).However, in the case of an element having the aforementioned π-typestructure, it is difficult to obtain a high thermoelectric powergeneration performance. Thus, it has not reached a level that issufficiently high enough to allow it to be used practically for morevarious applications. Furthermore, Bi₂Te₃ has a problem in heatresistance and therefore the thermoelectric power generation performancethereof deteriorates at temperatures of 100° C. or higher, and furtherBi₂Te₃ poses a heavy load on the environment since it contains Bi as aconstituent element.

In JP 2004-186241 A (Reference 1), boron compounds such as SrB₆ areexamined as materials for thermoelectric power generation. These boroncompounds are chemically very stable under normal temperature andpressure and are stable at temperatures up to around 1000K in the airand up to around 2500K under an atmosphere of an inert gas such asnitrogen. Thus they have excellent heat resistance. Furthermore, theaforementioned compounds are free from constituent elements that pose aheavy load on the environment. However, the boron compounds have a powerfactor of about 18 LiW/(cm·K²). When an element having theabove-mentioned π-type structure is formed using one of them, thethermoelectric power generation performance actually obtained from theelement further deteriorates, which prevents them from being usedpractically.

On the other hand, there has been a proposal for an element utilizinganisotropy of the thermoelectric properties in a laminated structurethat is naturally-occurring or is produced artificially as an elementhaving a different structure from the π-type structure (ThermoelectricsHandbook, Chapter 45 “Anisotropic Thermoelements”, CRC Press (2006):Reference 2). However, according to Reference 2, it is difficult toimprove ZT of such an element. Therefore, it is developed not for theuse for thermoelectric power generation but for assumed uses mainly inthe field of measurement such as an infrared sensor.

Furthermore, JP 6(1994)-310766 A (Reference 3) discloses, as athermoelectric material having a similar structure thereto, a materialin which a material having thermoelectric properties, which is typifiedby Fe—Si materials, and an insulating material with a thickness of 100nm or less, which is typified by SiO₂, are arranged alternately in theform of stripes on a substrate. According to Reference 3, in a materialhaving such a microstructure, as compared to the case where a Fe—Simaterial having thermoelectric properties is used independently, theSeebeck coefficient S can be improved but on the other hand, theelectrical resistivity p increases due to the insulating materialcontained therein. Accordingly, the element made thereof has increasedinternal resistance, and the electric power obtained therewith isreduced conversely.

Examples of other thermoelectric materials having laminated structuresinclude a material having a layered body formed of semimetal, metal, orsynthetic resin, which is disclosed in WO 00/076006 (Reference 4). Thismaterial is based on the configuration in which, as in the case of theconventional π-type structure, a temperature difference is applied tothe direction in which the respective layers of the layered body arelaminated, and thereby electric power is extracted through a pair ofelectrodes that are disposed so as to oppose in the same direction asthat described above. Therefore the element disclosed in Reference 4 issubstantially different from that disclosed in Reference 1.

SUMMARY OF THE INVENTION

As described above, in conventional thermoelectric materials, it is notpossible to obtain thermoelectric power generation performance that issufficiently high enough to allow them to be used practically for morevarious applications. Furthermore, there are demands for practicalapplication of a thermoelectric power generation element having athermoelectric material that poses less load on the environment.

The present inventors made studies assiduously with respect to thethermoelectric power generation element formed using a laminate. As aresult, they obtained the following unexpected findings to reach thepresent invention based thereon. That is, a laminate formed of a SrB₆layer (strontium boride) layer and a metal layer containing a specificmetal was used, with the thickness ratio between the SrB₆ layer and themetal layer being in a specific range, the lamination surfaces of thelaminate were inclined at a predetermined inclination angle θ withrespect to the direction in which electrodes, between which the laminatewas interposed, oppose each other, and thereby, as compared to the casewhere SrB₆ was used independently as a thermoelectric material, thepower factor of the element was increased and the thermoelectric powergeneration characteristics were improved considerably.

That is, an electric power generation method using a thermoelectricpower generation element of the present invention is a method forobtaining electric power from the element by applying a temperaturedifference in the thermoelectric power generation element. In thismethod, the element includes a first electrode and a second electrodethat are disposed to oppose each other, and a laminate that isinterposed between the first and second electrodes and that iselectrically connected to both the first and second electrodes, thelaminate has a structure in which a SrB₆ layer and a metal layercontaining Cu, Ag, Au, or Al are laminated alternately, a thicknessratio between the metal layer and the SrB₆ layer is in a range of metallayer: SrB₆ layer=20:1 to 2.5:1, and lamination surfaces of the SrB₆layer and the metal layer are inclined at an inclination angle θ of 20°to 50° with respect to the direction in which the first electrode andthe second electrode oppose each other. The method includes a step ofapplying a temperature difference in the direction perpendicular to thedirection in which the first electrode and the second electrode opposeeach other in the element, so that electric power is obtained throughthe first and second electrodes.

The thermoelectric power generation element of the present inventionincludes a first electrode and a second electrode that are disposed tooppose each other and a laminate that is interposed between the firstand second electrodes and that is electrically connected to both thefirst and second electrodes, where the laminate has a structure in whicha SrB₆ layer and a metal layer containing Cu, Ag, Au, or Al arelaminated alternately, a thickness ratio between the metal layer and theSrB₆ layer is in a range of metal layer: SrB₆ layer=20:1 to 2.5:1,lamination surfaces of the SrB₆ layer and the metal layer are inclinedat an inclination angle θ of 20° to 50° with respect to the direction inwhich the first electrode and the second electrode oppose each other,and a temperature difference applied in the direction perpendicular tothe direction in which the first electrode and the second electrodeoppose each other in the element generates a potential differencebetween the first and second electrodes.

A method of producing a thermoelectric power generation element of thepresent invention is a method of producing a thermoelectric powergeneration element that includes a first electrode and a secondelectrode that are disposed to oppose each other and a laminate that isinterposed between the first and second electrodes and that iselectrically connected to both the first and second electrodes, wherethe laminate has a structure in which a SrB₆ layer and a metal layercontaining Cu, Ag, Au, or Al are laminated alternately, a thicknessratio between the metal layer and the SrB₆ layer is in a range of metallayer: SrB₆ layer=20:1 to 2.5:1, lamination surfaces of the SrB₆ layerand the metal layer are inclined at an inclination angle θ of 20° to 50°with respect to the direction in which the first electrode and thesecond electrode oppose each other, and a temperature difference appliedin the direction perpendicular to the direction in which the firstelectrode and the second electrode oppose each other in the elementgenerates a potential difference between the first and secondelectrodes, wherein the method includes cutting out an original plate,in which a SrB₆ layer and a metal layer containing Cu, Ag, Au, or Al arelaminated alternately and a thickness ratio between the metal layer andthe SrB₆ layer is in a range of metal layer: SrB₆ layer=20:1 to 2.5:1,in a direction that obliquely traverses lamination surfaces of the SrB₆layer and the metal layer, and disposing the first and second electrodeson the laminate thus obtained so that the first and second electrodesoppose each other and the direction in which they oppose each othertraverses the lamination surfaces at an inclination angle θ of 20° to50°.

A thermoelectric power generation device of the present inventionincludes a support plate and a thermoelectric power generation elementdisposed on the support plate, where the element includes first andsecond electrodes that are disposed to oppose each other, and a laminatethat is interposed between the first and second electrodes and that iselectrically connected to both the first and second electrodes, thelaminate has a structure in which a SrB₆ layer and a metal layercontaining Cu, Ag, Au, or Al are laminated alternately, a thicknessratio between the metal layer and the SrB₆ layer is in a range of metallayer: SrB₆ layer=20:1 to 2.5:1, lamination surfaces of the SrB₆ layerand the metal layer are inclined at an inclination angle θ of 20° to 50°with respect to the direction in which the electrodes of a pair opposeeach other, the element is disposed on the support plate in such amanner that the direction perpendicular to the direction in which theelectrodes of a pair oppose each other agrees with the directionperpendicular to the surface of the support plate on which the elementis disposed, and a temperature difference is applied in the directionperpendicular to the surface of the support plate, so that electricpower is obtained through the electrodes of a pair.

According to the present invention, as compared to the case where SrB₆is used independently as a thermoelectric material, for example, thecase where an element having a π-type structure is formed, higherthermoelectric power generation characteristics can be obtained.Furthermore, the present invention makes it possible to obtain athermoelectric power generation method, a thermoelectric powergeneration element, and a thermoelectric power generation device thatpose less load on the environment. The present invention improves theefficiency of energy conversion between thermal energy and electricalenergy and has an effect of facilitating application of thermoelectricpower generation to various fields and thus has an industrially highvalue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a thermoelectric powergeneration element according to the present invention as well as thedirection in which the first and second electrodes oppose each other,the direction in which a temperature difference is to be applied, and aninclination angle θ.

FIG. 2 is a schematic view showing an example of the configuration fordriving the thermoelectric power generation element of the presentinvention.

FIG. 3 is a schematic view showing an example of the method of cuttingout a laminate from an original plate in a method of producing athermoelectric power generation element of the present invention.

FIG. 4 is a perspective view that schematically shows an example of thethermoelectric power generation device of the present invention.

FIG. 5 is a perspective view that schematically shows another example ofthe thermoelectric power generation device of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION <Thermoelectric PowerGeneration Element>

FIG. 1 shows an example of the thermoelectric power generation elementof the present invention. The thermoelectric power generation element 1shown in FIG. 1 includes a first electrode 11 and a second electrode 12that are disposed to oppose each other and a laminate 13 that isinterposed between the first electrode 11 and the second electrode 12and is electrically connected to both the electrodes. The laminate 13 isconnected to principal surfaces of the first electrodell and the secondelectrode 12, and the principal surfaces of both the electrodes are inparallel with each other. The shape of the laminate 13 shown in FIG. 1is rectangular parallelepiped, and the first electrode 11 and the secondelectrode 12 are disposed on a pair of opposing surfaces thereof. Thesurfaces of the first and second electrodes are orthogonal to thedirection (opposing direction 17) in which the first and secondelectrodes oppose each other.

The laminate 13 has a structure in which SrB₆ layers 14 and metal layers15 containing Cu (copper), Ag (silver), Au (gold), or Al (aluminum) arelaminated alternately. The lamination surfaces of the respective layers(the direction 16 that is in parallel with the principal surface of eachlayer) are inclined at an inclination angle θ of 20° to 50° with respectto the opposing direction 17. The thickness ratio between a metal layer15 and a SrB₆ layer 14 in the laminate 13 is in the range of metallayer: SrB₆ layer=20:1 to 2.5:1.

In the element 1, the temperature difference applied in the direction 18perpendicular to the opposing direction 17 generates a potentialdifference between the first electrode 11 and the second electrode 12.In other words, a temperature difference is applied in the direction 18perpendicular to the opposing direction 17 in the element 1, so thatelectric power can be extracted through the above-mentioned electrodesof a pair (the first electrode 11 and the second electrode 12).

Specifically, for example, as shown in FIG. 2, a temperature differenceis applied to the direction 18 perpendicular to the opposing direction17 in which the electrodes 11 and 12 oppose each other, with a hotsection 22 being attached closely to one surface of the laminate 13 ofthe element 1 where the electrodes 11 and 12 are not disposed and a coldsection 23 being attached closely to the other surface, thereby apotential difference is generated between the electrodes 11 and 12, andthus electric power can be extracted through both the electrodes. On theother hand, in a conventional thermoelectric power generation elementhaving a π-type structure, electromotive force is generated only in thedirection parallel to the direction in which the temperature differenceis applied and is not generated in the direction perpendicular thereto.Accordingly, in the conventional thermoelectric power generationelement, it is necessary to apply a temperature difference between thepair of electrodes, through which electric power is extracted. In theelement 1, both the opposing direction 17 in which the first electrode11 and the second electrode 12 oppose each other and the direction 18 inwhich the temperature difference is applied traverse the laminationsurfaces of the respective layers of the element 13. Furthermore, thedirection 18 in which the temperature difference is applied is notlimited as long as it is substantially perpendicular to the opposingdirection 17 in which the electrodes 11 and 12 oppose each other(similarly in this specification, the term “perpendicular” embraces“substantially perpendicular”).

Conventionally, as disclosed in Reference 3, it has been difficult toimprove both the Seebeck coefficient S and the electrical resistivity ρof the thermoelectric material and to increase the power factor of theelement. However, in the element 1, as compared to the case where SrB₆is used independently as the thermoelectric material, the power factorof the element can be increased and high thermoelectric power generationcharacteristics can be obtained.

The element 1 reflects the thermal properties of SrB₆ and therefore hasexcellent heat resistance.

The metal layer 15 contains Cu, Ag, Au, or Al. The metal layer 15contains preferably Cu, Ag, or Au and particularly preferably Cu or Ag.In this case, higher thermoelectric power generation characteristics canbe obtained. The metal layer 15 may contain such metal independently oras an alloy. When the metal layer 15 contains such metal independently,the metal layer 15 is composed of Cu, Ag, Au, or Al, preferably Cu, Ag,or Au, and particularly preferably Cu or Ag.

Preferably, a material with excellent electroconductivity is used forthe first electrode 11 and the second electrode 12. For example, it alsomay be metal such as Cu, Ag, Mo, W, Al, Ti, Cr, Au, Pt, or In, or anitride or oxide such as TiN, indium tin oxide (ITO), or SnO₂.Furthermore, for example, a solder, a silver solder, or anelectroconductive paste also can be used for the electrodes.

Although the detail is described in the section of Example, the presentinventors studied various conditions and found out that the power factorof the element 1 further was improved and higher thermoelectric powergeneration characteristics were obtained by controlling the inclinationangle θ formed between the lamination surfaces of the respective layersof the laminate 13 and the opposing direction 17 in which the electrodes11 and 12 oppose each other, and the thickness ratio between the SrB₆layer 14 and the metal layer 15.

The inclination angle θ is preferably 20° to 40° and more preferably 25°to 35°.

The thickness ratio between the metal layer 15 and the SrB₆ layer ispreferably in the range of metal layer: SrB₆ layer=20:1 to 4:1 and morepreferably in the range of metal layer: SrB₆ layer=10:1 to 4:1.

From the viewpoint of the combination of the inclination angle θ, thetype of the metal layer 15, and the thickness ratio, it is morepreferable that the inclination angle θ be 20° to 40°, the metal layer15 contain Cu, Ag, or Au, and the thickness ratio between the metallayer 15 and the SrB₆ layer 14 be in the range of metal layer: SrB₆layer=20:1 to 4:1.

From the same viewpoint, it is more preferable that the inclinationangle θ be 25° to 35°, the metal layer 15 contain Cu or Ag, and thethickness ratio between the metal layer 15 and the SrB₆ layer 14 be inthe range of metal layer: SrB₆ layer=10:1 to 4:1.

Depending on these conditions, the power factor (output factor) of theelement 1 can be at least 30 (μW/(cm·K²)), further can be at least 34(μW/(cm K²)) or at least 40 (μW/(cm·K²)).

<Method of Producing Thermoelectric Power Generation Element>

The thermoelectric power generation element 1 can be formed as follows.That is, for example, as shown in FIG. 3, an original plate (laminatedoriginal plate) 34, in which SrB₆ films 31 and metal films 32 containingCu, Ag, Au, or Al are laminated alternately and the thickness ratiobetween a metal film 32 and a SrB₆ film 31 is in the range of metalfilm: SrB₆ film=20:1 to 2.5:1, is cut out in a direction that obliquelytraverses the lamination surfaces 35 of the SrB₆ films 31 and the metalfilms 32 (for example, is cut out in such a manner that the angle formedbetween the cut out face and the lamination surfaces 35 is 20° to 50°),and the first and second electrodes are disposed on the resultantlaminate 13 (13 a, 13 b, 13 c, or 13 d) so as to oppose each other andso that the direction in which they oppose each other traverses thelamination surfaces 35 at an inclination angle θ of 20° to 50°. Themember indicated with numeral 33 in FIG. 3 is a laminate 33 that wasobtained by cutting out the original plate 34 so as to traverse thelamination surfaces 35 perpendicularly thereto. The thermoelectric powergeneration element of the present invention cannot be formed from such alaminate. The phrase “the first and second electrodes are disposed sothat the direction in which they oppose each other traverses thelamination surfaces 35” denotes that, for example, with respect to thelaminate 13 d shown in FIG. 3, the electrodes are disposed on the sidefaces A and A or the side faces B and B′.

The metal film 32 may be formed of metal that is identical to thatcomposing the metal layer 15.

The original plate 34 can be formed by, for example, superimposing SrB₆foils and metal foils alternately and bonding them together underpressure. In this case, the SrB₆ foils are formed into SrB₆ layers 31and the metal foils are formed into the metal layers 32. At the time ofbonding under pressure, heat may be applied in addition to pressure.When the SrB₆ foils are thin, they have low mechanical strength andtherefore tend to be damaged. Accordingly, it is preferable that metalfoils, each of which has a SrB₆ film formed on the surface thereofbeforehand, be used and they be bonded together under pressure. In thiscase, the original plate 34 with fewer defects tends to be obtained.Metal foils, each of which has the SrB₆ film formed on only one surfacethereof, may be used. However, when using metal foils, each of which hasthe SrB₆ film formed on each surface thereof, the degree of adhesionbetween the respective layers that compose the original plate 34 can beimproved.

Furthermore, for example, the original plate 34 also can be formed bydepositing the SrB₆ films and the metal films alternately.

Formation of the SrB₆ film on the surface of the metal foil anddeposition of the SrB₆ film and the metal film can be carried out byvarious thin film forming methods, for example, a sputtering method, anevaporation method, a laser ablation method, a vapor deposition methodsincluding a chemical vapor deposition method, a liquid phase growthmethod, or a plating method. The thickness ratio between the SrB₆ filmand the metal film that are formed by any one of the above-mentionedthin film formation techniques may be adjusted by a general method.

The thickness ratio between the metal layer 32 and the SrB₆ layer 31 inthe original plate 34 is preferably in the range of metal layer: SrB₆layer=20:1 to 4:1 and more preferably in the range of metal layer: SrB₆layer=10:1 to 4:1.

A known method such as a cutting process may be used for cutting out theoriginal plate 34. The surfaces of the laminate 13 obtained by cuttingout may be polished if necessary.

When the first and second electrodes are to be disposed, it is notalways necessary to dispose the electrodes on the whole surfaces of thelaminate 13 on which the electrodes are to be disposed. The electrodesmay be disposed on parts of the surfaces of the laminate 13 on which theelectrodes are to be disposed.

The method of disposing the first and second electrodes is notparticularly limited and various thin film formation techniques such asa sputtering method, an evaporation method, and a vapor growth method,or techniques of applying an electroconductive paste, plating, orspraying can be used. For example, electrodes formed separately may bejoined to the laminate 13 with, for example, a solder or a silversolder.

When the first and second electrodes are to be disposed on the laminate13, it is preferable that the first and second electrodes be disposed sothat the direction in which they oppose each other traverses thelamination surfaces 35 of the laminate 13 at an inclination angle of 20°to 40° and more preferably at an inclination angle of 25° to 35°.

<Thermoelectric Power Generation Device>

FIG. 4 shows an example of the thermoelectric power generation device ofthe present invention. The device 41 shown in FIG. 4 includes a supportplate 45 and six thermoelectric power generation elements 1 of thepresent invention disposed on the support plate 45. Each element 1 isdisposed on the support plate 45 in such a manner that the directionperpendicular to the direction 17 in which the first and secondelectrodes oppose each other in each element agrees with the directionperpendicular to the surface 46 of the support plate 45 on which theelements 1 are disposed. Furthermore, adjacent elements 1 are connectedelectrically in series with each other through a connecting electrode 43that also serves as the first or second electrode of each element 1.Extraction electrodes 44, each of which also serves as the first orsecond electrode, are disposed in elements 1 a and 1 b located on theends of the sequence of the six elements 1.

In the device 41, a temperature difference is allowed to be applied inthe direction perpendicular to the surface 46 of the support plate 45.For example, a cold section is brought into contact with the surface ofthe support plate 45 on which the elements 1 are not disposed, a hotsection is brought into contact with the opposite surface to the surfaceof the element 1 that is in contact with the support plate 45, andthereby electric power can be obtained through the extraction electrodes44. In the example shown in FIG. 4, in the adjacent elements 1, thedirections in which the lamination surfaces of the SrB₆ layers and themetal layers are inclined are opposite to each other. This is intendedto prevent the electromotive force generated in the elements 1 due tothe application of the temperature difference from being cancelledbetween the adjacent elements 1.

FIG. 5 shows another example of the thermoelectric power generationdevice of the present invention. The device 42 shown in FIG. 5 includesa support plate 45 and eight thermoelectric power generation elements 1of the present invention disposed on the support plate 45. Each element1 is disposed on the support plate 45 in such a manner that thedirection perpendicular to the direction 17 in which the first andsecond electrodes oppose each other in each element agrees with thedirection perpendicular to the surface 46 of the support plate 45 onwhich the elements 1 are disposed. The eight elements 1 are divided intofour blocks that are disposed on the support plate 45, with one blockincluding two elements 1. Elements of one block (for example, element 1a and 1 b) are connected electrically in parallel with each otherthrough a connecting electrode 43 that also serves as the first orsecond electrode of each element. The blocks adjacent to each other areconnected electrically in series through the connecting electrodes 43.

In the device 42, a temperature difference is allowed to be applied inthe direction perpendicular to the surface 46 of the support plate 45.For example, a cold section is brought into contact with the surface ofthe support plate 45 on which the elements 1 are not disposed, a hotsection is brought into contact with the opposite surface to the surfaceof the element 1 that is in contact with the support plate 45, andthereby electric power can be obtained through the extraction electrodes44. In the example shown in FIG. 5, the directions in which the SrB₆layers and the metal layers are inclined are identical to each other inthe elements 1 included in one block, and they are opposite to eachother in the adjacent blocks. This is intended to prevent theelectromotive force generated in the elements 1 due to the applicationof the temperature difference (generated in the blocks due to theapplication of the temperature difference) from being cancelled betweenthe adjacent elements 1 and between the adjacent blocks.

The configuration of the thermoelectric power generation device of thepresent invention is not limited to the examples shown in FIGS. 4 and 5.For example, one thermoelectric power generation element may be disposedon the support plate. However, when the thermoelectric power generationdevice is formed with at least two thermoelectric power generationelements being disposed as in the examples shown in FIGS. 4 and 5, moreelectrical energy can be obtained. Furthermore, as in the example shownin FIG. 4, when the elements are connected electrically in series witheach other, the voltage obtained is increased. As in the example shownin FIG. 5, when the elements are connected electrically in parallel witheach other, the possibility that the function of the thermoelectricpower generation device as a whole can be maintained even in the casewhere the electrical connection of the elements 1 is lost partially canbe increased and thus the reliability of the thermoelectric powergeneration device can be improved. That is, a suitable combination ofthe series and parallel connections of the elements makes it possible toconfigure a thermoelectric power generation device with highthermoelectric power generation characteristics.

The structures of the connecting electrodes 43 and the extractionelectrodes 44 are not particularly limited as long as they are excellentin electroconductivity. For example, the connecting electrodes 43 andthe extraction electrodes 44 may be formed of metal such as Cu, Ag, Mo,W, Al, Ti, Cr, Au, Pt, or In, or nitride or oxide such as TiN, indiumtin oxide (ITO), or SnO₂. Furthermore, a solder, a silver solder, or anelectroconductive paste also can be used for the electrodes.

<Electric Power Generation Method Using Thermoelectric Power GenerationElement>

The electric power generation method of the present invention is amethod of obtaining electric power through a first electrode 11 and asecond electrode 12 (or connecting electrodes 43 or extractionelectrodes 44), by applying a temperature difference in the directionperpendicular to the opposing direction 17 in which the electrodesoppose each other in a thermoelectric power generation element 1 of thepresent invention described above.

EXAMPLE

Hereinafter, the present invention is described in further detail. Thepresent invention is not limited to the following examples.

Example 1

In Example 1, thermoelectric power generation elements 1 as shown inFIG. 1 were produced using SrB₆ and several types of metals (Au, Ag, Cuand Al), and then the thermoelectric power generation characteristicsthereof were evaluated.

First, a metal foil (Au foil, Ag foil, Cu foil, or Al foil) with a sizeof 100 mm×100 mm and a thickness of 20 μm was prepared, and a 2.0-μmthick SrB₆ film was formed on each surface of the metal foil by thesputtering method.

Next, a sheet of a SrB₆ film /a metal foil /a SrB₆ film formed asdescribed above was cut into a size of 50 mm×50 mm to form small strippieces. Two hundred small pieces thus formed were superimposed togetherand were subjected to heat pressure bonding at 250° C. for one hourunder a reduced pressure of 10⁻⁴Pa while a load of 100 kg/cm² wasapplied in the direction in which they were laminated. Thereafter, itwas subjected to cutting and polishing and thus a laminated originalplate with a size of 3 mm×48 mm and a thickness of 20 mm was obtained.The section of the original palate thus obtained was observed with ascanning electron microscope (SEM). As a result, it was observed thatmetal layers (derived from the metal foils), each of which had athickness of about 18 Jim, and SrB₆ layers (derived from SrB₆ films),each of which had a thickness of about 2 μm, were laminated alternately.That is, the thickness ratio between the metal layer and the SrB₆ layerin the element 1 produced thereby was metal layer: SrB₆ layer=9:1.

The laminate 13 with a thickness of 1 mm, a width of 3 mm, and a lengthof 20 mm was cut out from the original plate obtained as described aboveby cutting with a diamond cutter as shown in FIG. 3, with theinclination angle θ being changed at 10° intervals from 0° to 90°.Thereafter, a first electrode 11 and a second electrode 12 made of Auwere formed, by the sputtering method, on the end faces (correspondingto the side faces B and B′ shown in FIG. 3) located in the direction ofthe long side of each laminate 13 cut out as described above. Thus eachthermoelectric power generation element 1 as shown in FIG. 1 wasobtained.

Next, as shown in FIG. 2, one surface of the element 1 on which theelectrodes were not disposed was heated to 150° C. with a heater and thesurface opposing thereto was maintained at 30° C. by water-cooling.Thus, a temperature gradient was applied in the direction perpendicularto the opposing direction 17, and the voltage (electromotive voltage)generated between the electrodes thereby and the electrical resistancevalue obtained between the electrodes were measured. Thus, the powerfactor of the element 1 was determined. The direction in which thetemperature gradient was applied was the direction that traversed thelamination surfaces of the SrB₆ layers and the metal layers in thelaminate 13.

Table 1 shows the results of evaluation of the power factors of therespective elements 1 with respect to the change in inclination angle θin the elements 1 (the elements 1 each have a metal layer of a Au layer,a Ag layer, a Cu layer, or an Al layer according to the type of themetal foil used therefor) formed using the respective metal foils. Forexample, in an element 1, with a metal layer being a Ag layer and theinclination angle θ being 30°, the electromotive voltage was 47 mV andthe electrical resistance value was 0.07 mΩ. The power factor determinedfrom those values was 43 (μW/(cm·K²)).

TABLE 1 [Change in power factor (μW/(cm · K²)) of elements according toinclination angle θ] Inclination angle θ (°) 0 10 20 30 40 50 60 70 8090 Au 0 14 28 31 27 20 12 6 2 0 Ag 0 23 41 43 36 27 16 8 2 0 Cu 0 21 3840 34 25 16 7 2 0 Al 0 10 22 25 22 16 10 5 1 0

As shown in Table 1, the power factor was not obtained with respect tothe elements with inclination angles θ of 0° and 90°, i.e. the elementsin which the lamination surfaces of the SrB₆ layers and the metal layerswere in parallel with or orthogonal to the direction in which the firstand second electrodes opposed each other. On the other hand, the powerfactors were obtained with respect to the elements with inclinationangles 0 other than 0° and 90°, i.e. the elements in which thelamination surfaces of the SrB₆ layers and the metal layers wereinclined with respect to the direction in which the first and secondelectrodes opposed each other. With respect to the elements withinclination angles 0 of 20° to 50°, high power factors were obtained,specifically, it was at least 16 (μW/(cm·K²)) when the metal forming themetal layers was Al, at least 20 (μW/(cm·K²)) when the metal forming themetal layers was Au, at least 25 (μW/(cm·K²)) when the metal forming themetal layers was Cu, and at least 27 (μW/(cm·K²)) when the metal formingthe metal layers was Ag.

Furthermore, when the inclination angle θ was 20° to 40°, higher powerfactors were obtained. Specifically, power factors as high as at least27 (μW/(cm·K²)) when the metal forming the metal layers was Au, Ag, orCu, and at least 34 (μW/(cm·K²)), in some cases, at least 40(μW/(cm·K²)) when the metal forming the metal layers was Ag or Cu wereobtained.

Example 2

In Example 2, Ag or Cu was used as the metal for forming a metal layerand elements with different thickness ratios between the metal layer andthe SrB₆ layer from one another were produced in the same manner as inExample 1. While the inclination angle θ was fixed at 30°, the thicknessof the metal foil used for forming the element was changed to 40 μm, 50μm, 60 μm, 70 μm, 80 μm, 90 μm, 95 μm, 98 μm, and 99 μm, and theelements were formed so that the lamination cycle of the metal layer andthe SrB₆ layer was 100 μm. The thickness ratios of the SrB₆ layers tothe laminates of the elements thus formed were 60%, 50%, 40%, 30%, 20%,10%, 5%, 2%, and 1%, respectively.

With respect to the elements thus produced, the power factors thereofwere evaluated in the same manner as in Example 1. The results thereofare indicated in Table 2.

TABLE 2 [Change in power factor (μW/(cm · K²)) of elements according tothickness ratio of SrB₆ layer to laminate] Thickness ratio of SrB₆ layerto laminate (%) 60 50 40 30 20 10 5 2 1 Ag 19 22 26 31 37 43 36 18 7 Cu19 21 25 30 36 40 33 16 6

As indicated in Table 2, when the thickness ratio of the SrB₆ layer tothe laminate was in the range of 5% to 30%, specifically in the range of5% to 20%, and particularly in the range of 10% to 20%, high powerfactors were obtained. When the thickness ratio was 10%, the highestpower factor was obtained. This trend was the same in both cases wherethe metal forming the metal layers was Ag and where it was Cu.

Example 3

In Example 3, while Cu was used as the metal for forming the metallayers, and elements that were different in the thickness ratio betweenthe metal layer and the SrB₆ layer and inclination angle θ from oneanother were produced in the same manner as in Example 1. Theinclination angle θ was changed at 50 intervals from 10° to 50°, thethickness of each Cu foil used for forming the elements was fixed at 20μm, the thickness of the SrB₆ film formed on the surface of the Cu foilwas changed to 0.25 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, and 8 μm. Thuselements were formed.

With respect to the elements thus produced, the power factors thereofwere evaluated in the same manner as in Example 1. The results are shownin Table 3 below.

TABLE 3 [Change in power factor (μW/(cm · K²)) of element in terms ofinclination angle θ and thickness ratio of SrB₆ layer to laminate: metalforming metal layer (thickness of 20 μm) was Cu] Inclination angle θ 1015 20 25 30 35 40 45 50 Thickness of SrB₆ 8 (μm)/ 23 30 32 32 30 28 2518 18 film when 29 (%) laminate was 4 (μm)/ 24 34 38 39 38 35 31 27 23formed (μm)/ 17 (%) Thickness ratio of 2 (μm)/ 20 31 38 40 40 38 34 3025 SrB₆ layer to 9 (%) laminate (%) 1 (μm)/ 13 22 29 32 33 32 30 27 23 5(%) 0.5 (μm)/ 4 8 11 14 16 16 16 14 13 2 (%) 0.25 (μm)/ 1 3 4 5 6 7 7 76 1 (%)

As indicated in Table 3, when the inclination angle θ was 20° to 50° andthe thickness of the SrB₆ film was in the range of 1 to 8 μm,particularly in the range of 1 to 4 μm, high power factors wereobtained. Particularly, when the thickness of the SrB₆ film was 2 μm(the thickness ratio between the Cu layer and the SrB₆ layer inlamination period of the element was 10:1), the highest power factor wasobtained.

Furthermore, when the results of this example is considered togetherwith those of Example 2, it is conceivable that the thermoelectric powergeneration characteristics of the elements depend considerably on thethickness ratio between the metal layer and the SrB₆ layer rather thanthe absolute values of their thicknesses. With respect to theinclination angle θ, high power factors, specifically, at least 34μW/(cm·K²) and at least 38 μW/(cm·K²) were obtained in the ranges of 20°to 40° and 25° to 35°, respectively (in both cases, the aforementionedthickness ratio was 10:1). In these cases, high thermoelectric powergeneration characteristics obtained thereby were approximately at leasttwice those obtained when SrB₆ was used independently as thethermoelectric material.

As described above, the present invention makes it possible to obtainhigher thermoelectric power generation characteristics as compared tothe case where SrB₆ is used independently as a thermoelectric material,for example, the case where an element having a π-type structure isformed. Furthermore, the present invention makes it possible to obtain athermoelectric power generation method, a thermoelectric powergeneration element, and a thermoelectric power generation device thatpose less load on the environment. The present invention improves theefficiency of energy conversion between thermal energy and electricalenergy and has an effect of facilitating application of thermoelectricpower generation to various fields and thus has an industrially highvalue.

Examples of promising applications include an electric generator thatutilizes exhaust gas heat from automobiles or factories, and a smallportable electric generator.

The present invention may be embodied in other forms without departingfrom the spirit and essential characteristics thereof. The embodimentsdisclosed in this specification are to be considered in all respects asillustrative and not limiting. The scope of the present invention isindicated by the appended claims rather than by the foregoingdescription, and all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

1. An electric power generation method using a thermoelectric powergeneration element for obtaining electric power from the element byapplying a temperature difference in the thermoelectric power generationelement, wherein the element comprises a first electrode and a secondelectrode that are disposed to oppose each other, and a laminate that isinterposed between the first and second electrodes and that iselectrically connected to both the first and second electrodes, thelaminate has a structure in which a SrB₆ layer and a metal layercontaining Cu, Ag, Au, or Al are laminated alternately, a thicknessratio between the metal layer and the SrB₆ layer is in a range of metallayer: SrB₆ layer=20:1 to 2.5:1, and lamination surfaces of the SrB₆layer and the metal layer are inclined at an inclination angle θ of 20°to 50° with respect to a direction in which the first electrode and thesecond electrode oppose each other, the method comprising applying atemperature difference in a direction perpendicular to the direction inwhich the first electrode and the second electrode oppose each other inthe element, so that electric power is obtained through the first andsecond electrodes.
 2. The electric power generation method using athermoelectric power generation element according to claim 1, whereinthe inclination angle θ of the lamination surfaces with respect to thedirection is 20° to 40°.
 3. The electric power generation method using athermoelectric power generation element according to claim 1, whereinthe inclination angle θ of the lamination surfaces with respect to thedirection is 25° to 35°.
 4. The electric power generation method using athermoelectric power generation element according to claim 1, whereinthe metal layer contains Cu, Ag, or Au.
 5. The electric power generationmethod using a thermoelectric power generation element according toclaim 1, wherein the metal layer contains Cu or Ag.
 6. The electricpower generation method using a thermoelectric power generation elementaccording to claim 1, wherein the thickness ratio between the metallayer and the SrB₆ layer is in a range of metal layer: SrB₆ layer=20:1to 4:1.
 7. The electric power generation method using a thermoelectricpower generation element according to claim 1, wherein the thicknessratio between the metal layer and the SrB₆ layer is in a range of metallayer: SrB₆ layer=10:1 to 4:1.
 8. The electric power generation methodusing a thermoelectric power generation element according to claim 1,wherein the element has a power factor of at least 30 (μW/(cm·K²)). 9.The electric power generation method using a thermoelectric powergeneration element according to claim 2, wherein the metal layercontains Cu, Ag, or Au, and the thickness ratio between the metal layerand the SrB₆ layer is in a range of metal layer: SrB₆ layer=20:1 to 4:1.10. The electric power generation method using a thermoelectric powergeneration element according to claim 3, wherein the metal layercontains Cu or Ag, and the thickness ratio between the metal layer andthe SrB₆ layer is in a range of metal layer: SrB₆ layer=10:1 to 4:1. 11.A thermoelectric power generation element, comprising: a first electrodeand a second electrode that are disposed to oppose each other, and alaminate that is interposed between the first and second electrodes andthat is electrically connected to both the first and second electrodes,where the laminate has a structure in which a SrB₆ layer and a metallayer containing Cu, Ag, Au, or Al are laminated alternately, athickness ratio between the metal layer and the SrB₆ layer is in a rangeof metal layer: SrB₆ layer=20:1 to 2.5:1, lamination surfaces of theSrB₆ layer and the metal layer are inclined at an inclination angle θ of20° to 50° with respect to a direction in which the first electrode andthe second electrode oppose each other, and a temperature differenceapplied in a direction perpendicular to the direction in which the firstelectrode and the second electrode oppose each other in the elementgenerates a potential difference between the first and secondelectrodes.
 12. The thermoelectric power generation element according toclaim 11, wherein the inclination angle θ of the lamination surfaceswith respect to the direction is 20° to 40°.
 13. The thermoelectricpower generation element according to claim 11, wherein the inclinationangle θ of the lamination surfaces with respect to the direction is 25°to 35°.
 14. The thermoelectric power generation element according toclaim 11, wherein the metal layer contains Cu, Ag, or Au.
 15. Thethermoelectric power generation element according to claim 11, whereinthe metal layer contains Cu or Ag.
 16. The thermoelectric powergeneration element according to claim 11, wherein the thickness ratiobetween the metal layer and the SrB₆ layer is in a range of metal layer:SrB₆ layer=20:1 to 4:1.
 17. The thermoelectric power generation elementaccording to claim 11, wherein the thickness ratio between the metallayer and the SrB₆ layer is in a range of metal layer: SrB₆ layer=10:1to 4:1.
 18. The thermoelectric power generation element according toclaim 11, wherein the element has a power factor of at least 30(μW/(cm·K²)).
 19. The thermoelectric power generation element accordingto claim 12, wherein the metal layer contains Cu, Ag, or Au, and thethickness ratio between the metal layer and the SrB₆ layer is in a rangeof metal layer: SrB₆ layer=20:1 to 4:1.
 20. The thermoelectric powergeneration element according to claim 13, wherein the metal layercontains Cu or Ag, and the thickness ratio between the metal layer andthe SrB₆ layer is in a range of metal layer: SrB₆ layer=10:1 to 4:1. 21.A method of producing a thermoelectric power generation element, theelement comprising: a first electrode and a second electrode that aredisposed to oppose each other, and a laminate that is interposed betweenthe first and second electrodes and that is electrically connected toboth the first and second electrodes, where the laminate has a structurein which a SrB₆ layer and a metal layer containing Cu, Ag, Au, or Al arelaminated alternately, a thickness ratio between the metal layer and theSrB₆ layer is in a range of metal layer: SrB₆ layer=20:1 to 2.5:1,lamination surfaces of the SrB₆ layer and the metal layer are inclinedat an inclination angle θ of 20° to 50° with respect to a direction inwhich the first electrode and the second electrode oppose each other,and a temperature difference applied in a direction perpendicular to thedirection in which the first electrode and the second electrode opposeeach other in the element generates a potential difference between thefirst and second electrodes, wherein the method comprises cutting out anoriginal plate, in which a SrB₆ layer and a metal layer containing Cu,Ag, Au, or Al are laminated alternately and a thickness ratio betweenthe metal layer and the SrB₆ layer is in a range of metal layer: SrB₆layer=20:1 to 2.5:1, in a direction that obliquely traverses laminationsurfaces of the SrB₆ layer and the metal layer, and disposing the firstand second electrodes on the laminate thus obtained so that the firstand second electrodes oppose each other and a direction in which theyoppose each other traverses the lamination surfaces at an inclinationangle θ of 20° to 50°.
 22. A thermoelectric power generation device,comprising: a support plate and a thermoelectric power generationelement disposed on the support plate, where the element includes firstand second electrodes that are disposed to oppose each other, and alaminate that is interposed between the first and second electrodes andthat is electrically connected to both the first and second electrodes,the laminate has a structure in which a SrB₆ layer and a metal layercontaining Cu, Ag, Au, or Al are laminated alternately, a thicknessratio between the metal layer and the SrB₆ layer is in a range of metallayer: SrB₆ layer=20:1 to 2.5:1, lamination surfaces of the SrB₆ layerand the metal layer are inclined at an inclination angle θ of 20° to 50°with respect to a direction in which the electrodes of a pair opposeeach other, the element is disposed on the support plate in such amanner that a direction perpendicular to the direction in which theelectrodes of a pair oppose each other agrees with a directionperpendicular to a surface of the support plate on which the element isdisposed, and a temperature difference is applied in the directionperpendicular to the surface of the support plate, so that electricpower is obtained through the electrodes of a pair.
 23. Thethermoelectric power generation device according to claim 22, whereinthe device includes at least two elements, each of which is identical tothe thermoelectric power generation element, and the elements areconnected electrically in series with each other through the electrodes.24. The thermoelectric power generation device according to claim 22,wherein the device includes at least two elements, each of which isidentical to the thermoelectric power generation element, and theelements are connected electrically in parallel with each other throughthe electrodes.